1. Field of the Invention
The present invention generally relates to a semiconductor device and a method for manufacturing a semiconductor device, and particularly relates to a semiconductor device of the leadless surface mounted type and a resin sealed type and a method for manufacturing such semiconductor device.
The pitch of the leads which are provided to a semiconductor of the resin sealed type needs to be ever smaller to achieve further miniaturization of electronic devices. Therefore, for the semiconductor device of the resin sealed type, new structures and manufacturing methods are required.
2. Description of the Related Art
FIGS. 1A-1C and FIG. 2 show cross-sectional diagrams of conventional resin sealed semiconductor devices.
In FIGS. 1A-1C, a semiconductor device includes a resin 1, a semiconductor chip 2, outer leads 3, bonding wires 4 and a die pad 5. This semiconductor device is of a package structure referred to as SSOP (Shrink Small Outline Package) wherein the outer leads 3 bent in a gull-wing shape are mounted to a carrying board.
In FIG. 2, a semiconductor device includes the resin 1, the semiconductor chip 2, the bonding wires 4, solder balls 6 and a carrying board 7 for mounting the semiconductor chip 2. This semiconductor device is of a package structure referred to as BGA (Ball Grid Array) wherein terminal parts to be mounted to a carrying board are formed of the solder balls 6.
In the SSOP-type semiconductor device shown in FIG. 1, the area of a connecting part 9 ranging from the inner leads 8 to the outer leads 3, shown in resin 1, and/or the area occupied by the outer leads 3 is large, so that a problem arises in that the device occupies a large area when it is mounted on a board. Also, in the BGA-type semiconductor device shown in FIG. 2, the manufacturing cost increases due to the use of the carrying board 7.
A semiconductor device which could overcome the above-mentioned problems is described in Japanese Patent Application No.7-322803. FIG. 3 shows a semiconductor device 110 disclosed in the above application. As shown in FIG. 3, the semiconductor device 110 has a very simple structure including a semiconductor chip 111, a resin package 112 and metal layers 113. The semiconductor device 110 is characterized in that resin protrusions 117 formed as part of the mounting surface 116 of the resin package 112 are coated with the metal layers 113.
In the semiconductor device 110 constructed as described above, no inner lead or outer lead, as used in a conventional SSOP, is necessary. Therefore, the connecting area from inner leads to outer leads and the area occupied by the outer leads become unnecessary, so that the semiconductor device 110 is miniaturized. Also, the manufacturing cost of the semiconductor device 110 is reduced since there is no need for using the carrying board to form solder balls, as were necessary in conventional BGA. In addition, the resin protrusions 117 and the metal layers 113 together provide a function equivalent to that of solder bumps (protruded electrode) of the semiconductor device of the BGA type. This makes it easier to mount the semiconductor device.
As described above, the semiconductor device 110 can bring about various advantageous effects which were not obtained by semiconductor devices of the prior art shown in FIG. 1 and in FIG. 2.
However, the semiconductor device 110 has a structure in which the metal layers 113 are simply disposed to cover the resin protrusions 117. At junction parts between the metal layers and the resin protrusions 117, it is difficult to maintain a sufficient joining force. There were problems such that for example during the semiconductor manufacturing process or when mounting, the metal layers 113 peel off from the resin protrusions 117 and reliability of the semiconductor device 110 may decrease.
Accordingly, there is a need for a semiconductor device and a method of manufacturing a semiconductor device which overcomes the above problems. Also, there is a need for a semiconductor device in which reliability is improved by firmly joining the metal layers and the resin protrusions and a method of manufacturing such semiconductor device.